Various medical conditions are characterized by accumulation of liquids under or behind the skin surface. Such conditions may include otitis media, pressure ulcers, or other types of deep tissue injury under intact skin.
Medications or other substances may be introduced or delivered into the bloodstream. For example, a substance may be delivered orally to a patient, or may be injected into tissue or via an intravenous infusion. In some cases, it is important to monitor the concentration or amount of the substance in a patient's blood or tissue. Monitoring the concentration or the amount may include drawing a blood or tissue sample from the patient.